The present invention relates to an rpm-governing system for an internal combustion engine with auto-ignition having an electromagnetic final control element influencing the quantity of fuel to be injected, at least in the event of idling, a control unit including, preferably, a PID regulator and an actual rpm value/set-point rpm value deviation detector for forming, together with the control unit, a final control element trigger signal.
In internal combustion engines with auto-ignition, it is known to govern the rpm by means of a PID regulator and to carry the output signal of this regulator to an electromagnetic final control element connected to the regulator rod of the fuel pump of the engine. Although this known system is capable of providing generally satisfactory results, still, both the governing of the idling rpm and the transition into overrunning involve certain difficulties, especially when the engine is cold. That is because when the engine is cold, the rpm drop that occurs when pressure on the driving pedal is released is quite severe, and low amplitude oscillations in the rpm signal can cause the engine to stall. The possibility of counteracting these severe changes in rpm by means of an appropriate D component of the regulator does exist; but the danger then is that interference factors thereby introduced may affect the result of regulation.